Firefighters responded to reports of the fire at 10:30 p.m. Saturday after smoke filled the tunnel between the South Station and Broadway stops. Power to the tracks was shut down a short time later so that crews could fix damaged electrical cables.

Buses are taking passengers from the JFK and Park Street station stops while crews work.

MBTA spokesman Joe Pesaturo said crews would continue to work through Monday and hope to have service fully functional by Tuesday’s commute.